System and Method for Detecting Lockup Clutch On-Coming Capacity

ABSTRACT

A dynamic model is stored in memory that defines torque transmitted by a lockup clutch in a torque converter as a function of a plurality of torque converter operating parameters. A lockup clutch command to control engagement the lockup clutch is asserted, and thereafter a number of the plurality of torque converter operating parameters are monitored. The model is continually solved using the monitored operating parameters to determine torque transmitted by the lockup clutch over time, and a lockup clutch on-coming capacity signal is produced if the torque transmitted by the lockup clutch exceeds a torque threshold.

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims priority to, and the benefit of, U.S.Provisional Patent Application No. 61/045,126 filed Apr. 15, 2008, thedisclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to torque converters that serveas interfaces between internal combustion engines and automatictransmissions in mobile vehicles, and more specifically to the controlof lockup clutches in such torque converters.

BACKGROUND

Torque converters are commonly used as an interface between an internalcombustion engine and a transmission having a number of automaticallyselectable gear ratios. Some torque converters include a so-calledlockup clutch that is connected between the pump and turbine of thetorque converter, and that is engaged under certain operating conditionsto rigidly connect the pump and turbine together. It is desirable to beable to detect, during engagement of the lockup clutch, when the lockupclutch is transmitting at least a discernable amount of torque.

SUMMARY

The present invention may comprise one or more of the features recitedin the attached claims, and/or one or more of the following features andcombinations thereof. In a torque converter having a pump that isrotatably driven by an internal combustion engine and that is fluidlycoupled to a turbine, and a lockup clutch connected between pump and theturbine, a method for detecting lockup clutch on-coming capacity maycomprise retrieving from memory a dynamic model that defines torquetransmitted by the lockup clutch as a function of a plurality of torqueconverter operating parameters, asserting a lockup clutch command tocontrol engagement the lockup clutch, monitoring a number of theplurality of torque converter operating parameters after asserting thelockup clutch command, continually solving the model using the monitoredoperating parameters to determine torque transmitted by the lockupclutch over time, and producing a lockup clutch on-coming capacitysignal if the torque transmitted by the lockup clutch exceeds a torquethreshold.

The lockup clutch command may comprise a fill phase followed by aninitial lockup clutch activation value. Monitoring a number of theplurality of torque converter operating parameters and continuallysolving the model may be carried out after the initial lockup clutchactivation value is asserted. The method may further comprisedetermining inertia of the engine, and one of the plurality of torqueconverter operating parameters included in the model may accordingly bethe inertia of the engine. Monitoring a number of the plurality oftorque converter operating parameters may comprise monitoring torqueapplied by the engine to the pump, monitoring rotational speed of thepump, determining angular acceleration of the pump based on themonitored rotational speed of the pump and monitoring rotational speedof the turbine, and the model may define torque transmitted by thelockup clutch as a function of the inertia of the engine, the torqueapplied by the engine to the pump, the rotational speeds of the pump andthe turbine and the angular acceleration of the pump. The method mayfurther comprise determining torque transmitted by the pump as afunction of the rotational speed of the pump and the rotational speed ofthe turbine. In one embodiment, the dynamic model may define torquetransmitted by the lockup clutch according to the equation:T_(LU)=T_(E)−T_(P)−(I_(E)*PA), where T_(LU) is the torque transmitted bythe lockup clutch, T_(E) is the torque applied by the engine to thepump, T_(P) is the torque transmitted by the pump, I_(E) is the inertiaof the engine and PA is the angular acceleration of the pump.Alternatively, the method may further comprise determining an initialvalue of the rotational speed of the pump during the fill phase of thelockup clutch command, determining an initial value of the rotationalspeed of the turbine during the fill phase of the lockup clutch command,receiving an initial value of a reported engine output torque producedby a controller during the fill phase of the lockup clutch command,wherein the controller is configured to control operation of the engine,and determining a torque offset value as a function of the initialvalues of the rotational speed of the pump, the rotational speed of theturbine and the reported engine output torque. Monitoring torque appliedby the engine to the pump may comprise monitoring reported engine outputtorque produced by the controller after the initial lockup clutchactivation value is asserted and computing a compensated engine outputtorque as a function of the torque offset value and the reported engineoutput torque produced by the controller after the initial lockup clutchactivation value is asserted. In this embodiment, the dynamic model maydefine torque transmitted by the lockup clutch according to theequation: T_(LU)=T_(EC)−T_(P)−(I_(E)*PA), where T_(LU) is the torquetransmitted by the lockup clutch, T_(EC) is the compensated engineoutput torque, T_(P) is the torque transmitted by the pump, I_(E) is theinertia of the engine and PA is the angular acceleration of the pump.

In a torque converter having a pump that is rotatably driven by aninternal combustion engine and that is fluidly coupled to a rotatableturbine, and a lockup clutch connected between pump and the turbine, amethod for detecting lockup clutch on-coming capacity may comprisedetermining an inertia of the engine, monitoring torque applied by theengine to the pump, monitoring torque transmitted by the pump,monitoring angular acceleration of the pump, continually computingtorque transmitted by the lockup clutch as a function of the inertia ofthe engine, the torque applied by the engine to the pump, the torquetransmitted by the pump, and the angular acceleration of the pump, andproducing a lockup clutch on-coming capacity signal if the torquetransmitted by the lockup clutch exceeds a torque threshold.

The method may further comprise asserting a lockup clutch command toengage the lockup clutch. The lockup clutch command may include a fillphase followed by an initial lockup clutch activation value. Monitoringtorque applied by the engine to the pump, monitoring torque transmittedby the pump, monitoring angular acceleration of the pump and continuallycomputing torque transmitted by the lockup clutch may all carried outafter asserting the initial lockup clutch activation value.

In one embodiment, continually computing torque transmitted by thelockup clutch may comprise continually computing the torque according tothe equation: T_(LU)=T_(E)−T_(P)−(I_(E)*PA), where T_(LU) is the torquetransmitted by the lockup clutch, T_(E) is the torque applied by theengine to the pump, T_(P) is the torque transmitted by the pump, I_(E)is the inertia of the engine and PA is the angular acceleration of thepump.

In an alternative embodiment, the method may further comprisedetermining a compensated torque value as a function of a torque offsetvalue and a reported engine output torque produced by a controllerconfigured to control operation of the engine, and the torque applied bythe engine to the pump may be the compensated torque value.Illustratively, the torque offset value may be determined by determiningan initial pump rotational speed and an initial turbine rotational speedduring the fill phase of the lockup clutch command, computing an initialpump torque as a function of the initial pump and turbine rotationalspeeds, determining an initial value of the reported engine outputtorque during the fill phase of the lockup clutch command, and computingthe torque offset value as a function of the initial pump torque and theinitial value of the reported engine output torque. In this embodiment,continually computing torque transmitted by the lockup clutch maycomprise continually computing the torque according to the equation:T_(LU)=T_(EC)−T_(P)−(I_(E)*PA), where T_(LU) is the torque transmittedby the lockup clutch, T_(EC) is the compensated torque value, T_(P) isthe torque transmitted by the pump, I_(E) is the inertia of the engineand PA is the angular acceleration of the pump.

In either case, the method may further comprise monitoring rotationalspeed of the pump, and monitoring rotational speed of the turbine.Monitoring torque transmitted by the pump may comprise determining thetorque transmitted by the pump as a function of the rotational speed ofthe pump and the rotational speed of the turbine. Determining inertia ofthe engine may comprise receiving a reported engine inertia valueproduced by a control circuit configured to control operation of theengine. Alternatively, determining inertia of the engine may compriseretrieving a stored engine inertia value from memory.

A system for detecting lockup clutch on-coming capacity in a torqueconverter may comprise a turbine engaging an input shaft of atransmission, a pump engaging an output shaft of an internal combustionengine and fluidly coupled to the turbine, the lockup clutch connectedbetween the pump and the turbine, a first sensor configured to produce apump speed signal corresponding to a rotational speed of the pump, asecond sensor configured to produce a turbine speed signal correspondingto a rotational speed of the turbine, and a control circuit including amemory having instructions stored therein that are executable by thecontrol circuit to compute angular acceleration of the pump as afunction of the pump speed signal, to compute torque transmitted by thelockup clutch as a function of the pump speed signal, the turbine speedsignal, an inertia of the engine, an output torque produced by theengine and the angular acceleration of the pump, and to produce a lockupclutch on-coming capacity signal if the torque transmitted by the lockupclutch exceeds a threshold torque.

The system may further comprise an actuator configured to be responsiveto a lockup clutch activation command to control engagement of thelockup clutch. The instructions stored in the memory may further includeinstructions that are executable by the control circuit to produce thelockup clutch activation command, wherein the lockup clutch activationcommand comprises a fill phase followed by an initial lockup clutchactivation value. The instructions stored in the memory may furtherinclude instructions that are executable by the control circuit to begincomputing the torque transmitted by the lockup clutch and comparing thetorque transmitted by the lockup clutch to the threshold torque afterthe initial lockup clutch activation value is asserted. The system mayfurther comprise an engine controller configured to control, at least inpart, operation of the engine. The control circuit may be configured toreceive engine output torque values, corresponding to torque produced bythe engine, from the engine controller. The system may further comprisea data link established between a communication port of the controlcircuit and a communication port of the engine controller. The enginecontroller may be configured to supply the engine output torque valuesto the data link in the form of engine output torque messages. Thecontrol circuit may be configured to retrieve the engine output torquemessages from the data link.

The instructions stored in the memory may include instructions that areexecutable by the control circuit to process the engine output torquemessages to determine the output torque produced by the engine. Theinstructions stored in the memory include instructions that areexecutable by the control circuit to compute torque transmitted by thepump as a function of the pump speed signal and the turbine speedsignal, and to compute the torque transmitted by the lockup clutchaccording to the equation: T_(LU)=T_(E)−T_(P)−(I_(E)*PA) where T_(LU) isthe torque transmitted by the lockup clutch, T_(E) is the output torqueproduced by the engine, T_(P) is the torque transmitted by the pump,I_(E) is the inertia of the engine and PA is the angular acceleration ofthe pump.

The instructions stored in the memory may further include instructionsthat are executable by the control circuit to process at least one ofthe engine output torque messages to determine an initial engine outputtorque value, determine from the pump speed signal an initial pump speedand determine from the turbine speed signal an initial turbine speed allduring the fill phase of the lockup clutch activation command, and tothen compute a torque offset value as a function of the initial engineoutput torque value, the initial pump speed and the initial turbinespeed. The instructions stored in the memory may further includeinstructions that are executable by the control circuit to determine theoutput torque produced by the engine after the initial lockup clutchactivation value is asserted by processing the engine output torquemessages to determine corresponding engine output torque values, andthen computing the output torque produced by the engine in the form of acompensated engine output torque as a function of the engine outputtorque values and the torque offset value. The instructions stored inthe memory may include instructions that are executable by the controlcircuit to compute torque transmitted by the pump as a function of thepump speed signal and the turbine speed signal, and to compute thetorque transmitted by the lockup clutch according to the equation:T_(LU)=T_(EC)−T_(P)−(I_(E)*PA), where T_(LU) is the torque transmittedby the lockup clutch, T_(EC) is the compensated engine output torque,T_(P) is the torque transmitted by the pump, I_(E) is the inertia of theengine and PA is the angular acceleration of the pump.

The engine controller may be configured to supply an inertia valuecorresponding to the inertia of the engine to the data link in the formof an engine inertia message. The control circuit may be configured toretrieve the inertia message from the data link and process the inertiamessage to determine the inertia of the engine. Alternatively, thememory may have stored therein a value of the inertia of the engine. Theinstructions stored in the memory may further include instructions thatare executable by the control circuit to determine the inertia of theengine by retrieving the value of the inertia of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram and schematic view of one illustrativeembodiment of a system for controlling operation of a lock up clutch ina torque converter.

FIG. 2 is a flowchart of one illustrative embodiment of a process forcontrolling lock up clutch operation.

FIG. 3 is a plot of a number of operating parameters associated withlock up clutch operation.

FIG. 4 is a flowchart of one illustrative embodiment of a process fordetecting lockup clutch on-coming capacity.

FIG. 5 is a flowchart of one illustrative embodiment of a process forcontrolling engagement of the lock up clutch following detection oflockup clutch on-coming capacity.

FIG. 6 is a flowchart of one illustrative embodiment of a process fordetermining pump shaft speed and acceleration profiles for use with theprocess of FIG. 5.

FIG. 7 is a flowchart of one illustrative embodiment of a process formanaging accumulator effects during the process of FIG. 5.

FIG. 8 is a plot of a number of operating parameters associated withlock up clutch operation during the accumulator management process ofFIG. 7.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to a number of illustrativeembodiments shown in the attached drawings and specific language will beused to describe the same.

Referring now to FIG. 1, a block diagram and schematic view of oneillustrative embodiment of a system 10 for controlling operation of alock up clutch in a torque converter is shown. In the illustratedembodiment, the system 10 includes an internal combustion engine 12 thatis configured to rotatably drive an output shaft 14 that is coupled toan input or pump shaft 16 of a conventional torque converter 20. Theinput or pump shaft 16 is attached to an impeller or pump 18 that isrotatably driven by the output shaft 14 of the engine 12. The torqueconverter 20 further includes a turbine 22 that is attached to a turbineshaft 24, and the turbine shaft 24 is coupled to, or integral with, arotatable input shaft 26 of a transmission 28. The transmission 28 isconventional and includes a number of automatically selected gearratios. An output shaft 30 of the transmission is coupled to, androtatably drives, a number of wheels (not shown) of a vehicle carryingthe engine 12, torque converter 20 and transmission 28.

A conventional lockup clutch 32 is connected between the pump 18 and theturbine 22, and the lockup clutch 32 is fluidly coupled to a fluidactuator 36 via a fluid passageway 34. The operation of the torqueconverter 20 is conventional in that the torque converter 20 is operablein a so-called “torque converter” mode during certain operatingconditions such as vehicle launch, low speed and certain gear shiftingconditions. In the torque converter mode, the lockup clutch 32 isdisengaged and the pump 18 rotates at the rotational speed of the engineoutput shaft 14 while the turbine 22 is rotatably actuated by the pump18 through a fluid (not shown) interposed between the pump 18 and theturbine 22. In this operational mode, torque multiplication occursthrough the fluid coupling such that the turbine shaft 24 is exposed tomore drive torque than is being supplied by the engine 12, as is knownin the art. The torque converter 20 is alternatively operable in aso-called “lockup” mode during other operating conditions, such as whencertain gear ratios of the transmission 28 are engaged. In the lockupmode, the lockup clutch 32 is engaged and the pump 18 is thereby securedto directly to the turbine 22 so that the engine output shaft 14 isdirectly coupled to the input shaft 26 of the transmission 28, as isalso known in the art.

The system 10 further includes a transmission control circuit 40 thatincludes a memory unit 42 and a conventional timer circuit 44. Thetransmission control circuit 40 is illustratively microprocessor-based,and the memory unit 42 generally includes instructions stored thereinthat are executable by the transmission control circuit 40 to controloperation of the torque converter 20 and the transmission 28. It will beunderstood, however, that this disclosure contemplates other embodimentsin which the transmission control circuit 40 is notmicroprocessor-based, but is configured to control operation of thetorque converter 20 and/or transmission 28 based on one or more sets ofhardwired instructions and/or software instructions stored in the memoryunit 42.

In the system 10 illustrated in FIG. 1, the torque converter 20 and thetransmission 28 each include one or more sensors configured to producesensor signals that are indicative of one or more operating states ofthe torque converter 20 and/or the transmission 28. For example, thetorque converter 20 includes the conventional speed sensor 50 that ispositioned and configured to produce a speed signal corresponding to therotational speed of the torque converter pump shaft 16 (which is alsothe rotational speed of the output shaft 14 of the engine 12). The speedsensor 50 is electrically connected to a pump speed input, PS, of thetransmission control circuit 40 via a signal path 52, and thetransmission control circuit 40 is operable to process the speed signalproduced by the speed sensor 50 in a conventional manner to determinethe rotational speed of the pump shaft 16. The transmission 28 furtherincludes a second speed sensor 54 that is positioned and configured toproduce a speed signal corresponding to the rotational speed of theinput shaft 26 of the transmission 28. The input shaft 26 of thetransmission 28 is directly coupled to, or integral with, the turbineshaft 24, and the speed sensor 54 may alternatively be positioned andconfigured to produce a speed signal corresponding to the rotationalspeed of the turbine shaft 24. In any case, the speed sensor 54 may beconventional, and is electrically connected to a turbine speed input,TS, of the transmission control circuit 40 via a signal path 56. Thetransmission control circuit 40 is configured to process the speedsignal produced by the speed signal 54 in a conventional manner todetermine the rotational speed of the turbine shaft 24/input shaft 26 ofthe transmission 28.

In the illustrated embodiment, the transmission 28 further includes oneor more actuators configured to control various operations within thetorque converter 20 and/or transmission 28. For example, thetransmission 28 includes an actuator 36 that is electrically connectedto a lockup clutch command output, LCC, of the transmission controlcircuit 40 via a signal path 62. The actuator 36 is responsive to thelockup clutch command signal, LCC, produced by the transmission controlcircuit 40 on the signal path 62 to control the pressure of fluid withinthe fluid passageway 34, and thus the actuating pressure supplied to thelockup clutch 32. Illustratively, the actuator 36 may be provided in theform of a conventional charge pump fluidly coupled to a source of fluid,e.g., transmission oil, although this disclosure contemplates otherembodiment in which the actuator may alternatively be provided in theform of a conventional valve, pump or the like, that is fluidly coupledto a source of fluid, e.g., transmission oil.

In the illustrated embodiment, the system 10 further includes an enginecontrol circuit 66 having an input/output port (I/O) that iselectrically coupled to the engine 12 via a number, M, of signal paths,wherein M may be any positive integer. The engine control circuit 66 maybe conventional, and is operable to control and manage the overalloperation of the engine 12. The engine control circuit 66 furtherincludes a communication port, COM, that is electrically connected to asimilar communication port, COM, of the transmission control circuit 40via a number, N, of signal paths 64, wherein N may be any positiveinteger. The one or more signal paths 64 are typically referred tocollectively as a data link. Generally, the engine control circuit 66and the transmission control circuit 40 are operable to shareinformation via the one or more signal paths 64 in a conventionalmanner. In one embodiment, for example, the engine control circuit 66and transmission control circuit 40 are operable to share informationvia the one or more signal paths 64 in the form of one or more messagesaccordance with a society of automotive engineers (SAE) J-1939communications protocol, although this disclosure contemplates otherembodiments in which the engine control circuit 66 and the transmissioncontrol circuit 40 are operable to share information via the one or moresignal paths 64 in accordance with one or more other conventionalcommunication protocols.

As it relates to this disclosure, the transmission control circuit 40 isoperable to receive certain operating information relating to operationof the engine 12 from the engine control circuit 66 via the one or moresignal paths 64 in a conventional manner. For example, the enginecontrol circuit 66 is configured in a conventional manner to determinethe instantaneous output torque produced by the engine 12, and in theillustrated embodiment the engine control circuit 66 is operable tosupply the instantaneous engine output torque information to thetransmission control circuit 40 via the one or more signal paths 64,such as in the form of a message that the transmission control circuit40 may process to determine a corresponding engine output torque value.As another example, the engine control circuit 66 is operable in aconventional manner to determine the rotational speed of the engineoutput shaft 14, and in one embodiment the engine control circuit 66 isoperable to supply the engine rotational speed information to thetransmission control circuit 40 via the one or more signal paths 64. Inthis embodiment, the speed sensor 50 described hereinabove is notnecessary, and may be omitted or otherwise be unused. Alternatively, thetransmission control circuit 40 may be configured to determine therotational speed of the engine 12 using both the signal produced by thesensor 50 and the engine rotational speed information supplied by theengine control circuit 66 via the one more signal paths 64.

Referring now to FIG. 2, a flow chart is shown of one illustrativeembodiment of a process 100 for controlling operation of the lockupclutch 32. The process 100 is illustratively stored in the memory unit42 of the transmission control circuit 40 in the form of one or moresets of instructions that are executable by the transmission controlcircuit 40 to control operation of the lockup clutch 42. The process 100will be described with the aid of the plot of FIG. 3, which shows anumber of operating parameters (arbitrary scale) over time (seconds). Inparticular, the plot of FIG. 3 shows engine output torque 120 (e.g.,supplied to the transmission control circuit 40 by the engine controlcircuit 66), engine (pump shaft) speed 122 (e.g., produced by the speedsensor 50), turbine speed 126 (e.g., produced by the speed sensor 54)and lockup clutch pressure 128 (e.g., produced by the pressure sensor58). Other signals and/or features are also shown in the plot of FIG. 3,and such other signals and/or signal features will be describedhereinafter within the context of the process 100.

The process 100 begins at step 102, and thereafter at step 104 thetransmission control circuit 40 is operable to determine if the lockupclutch command, LCC, has been asserted, i.e., is active. In theillustrated embodiment, the transmission control circuit 40 is operableto produce the lockup clutch command, LCC, according to one or more setsof instructions stored in the memory 42, and therefore has knowledge ofthe state of the lockup clutch command, LCC. If the transmission controlcircuit 40 determines at step 104 that the lockup clutch command, LCC,has not been asserted, the process 100 loops back to step 104. If, onthe other hand, the transmission control circuit 40 determines at step104 that the lockup clutch command, LCC, has been asserted, execution ofthe process 100 advances to step 106 where the transmission controlcircuit 40 is operable to determine initial pump and turbine shaftrotational speeds, PS_(i) and TS_(i), and initial engine output torque,T_(Ei) during the fill phase of the lockup clutch command, LCC.

Referring to FIG. 3, lockup clutch pressure is represented by thewaveform 128, and the lockup clutch pressure 128 generally follows thelockup clutch command, LCC. The wave form 128 thus represents the lockupclutch command, LCC, and the waveform 128 will be used herein toillustrate and described the operation of LCC. In any case, the lockupclutch command 128 illustrated in FIG. 3 includes a conventional fillphase followed by a controlled pressure increase until engagement of thelockup clutch 32 is achieved. The fill phase of the lockup clutchcommand 128 follows assertion of the lockup clutch command, and isidentified by a rapid increase to a peak pressure 130 for a shortduration followed by a rapid decrease in pressure to an initial pressurevalue or initial lockup clutch activation value 132. The fill phase isused in a conventional manner to cause the piston (not shown) of thelockup clutch 32 to travel rapidly toward, but not contact, a pistonstop (not shown) defined by the lockup clutch 32 under high fluidpressure conditions. Following the fill phase, the lockup clutchpressure 128 is then controllably increased from the initial pressurevalue or initial lockup clutch activation value 132 to achieveengagement of the lockup clutch 32.

Referring again to FIG. 2, the transmission control circuit 40 isillustratively operable at step 106 to determine the initial pump shaftrotational speed TS_(i), by monitoring the speed signal produced by thespeed sensor 50. Alternatively or additionally, the transmission controlcircuit 40 may be operable at step 106 to determine the pump shaftrotational speed PS_(i), based on engine rotational speed informationsupplied by the engine control circuit 66 to the transmission controlcircuit 40 via the one or more signal paths 64. The transmission controlcircuit 40 is illustratively operable at step 106 to determine theturbine shaft rotational speed, TS_(i), by monitoring the speed signalproduced by the speed sensor 54. The transmission control circuit 40 isfurther illustratively operable at step 106 to determine the initialengine output torque value T_(Ei), by receiving the engine output torqueinformation supplied by the engine control circuit 66 on the one or moresignal paths 64. Illustratively, the transmission control circuit 40 isoperable to determine PS_(i), TS_(i) and T_(Ei), during an initialportion of the fill phase, e.g., just after the peak pressure 130 isachieved, although this disclosure contemplates alternate embodiments inwhich the transmission control circuit 40 is operable to determinePS_(i), TS_(i) and T_(Ei), during one or more other portions of the fillphase, and/or during one or more other portions of the lockup clutchcommand, LCC, that follow the fill phase.

Following step 106, the transmission control circuit 40 is operable atstep 108 to compute an initial pump shaft torque, T_(Pi), as a functionof the initial pump and turbine shaft rotational speed values, PS_(i)and TS_(i) respectively. In one embodiment, the transmission controlcircuit 40 is operable to compute the initial pump shaft torque value,T_(Pi) according to the formula T_(Pi)=a*PS_(i)²+b*PS_(i)*TS_(i)+c*TS_(i) ², although the transmission control circuit40 may be alternatively operable at step 108 to compute the initial pumpshaft torque value T_(Pi) using one or more other conventional functionsof PS_(i) and TS_(i) or as functions of more, fewer and/or differenttorque converter 20 and/or transmission 28 operating parameters. In anycase, the process 100 advances from step 108 to step 110 where thetransmission control circuit 40 is operable to compute an engine outputtorque offset value, ΔT_(i) according to the equationΔT_(i)=T_(Pi)−T_(Ei).

Following step 110, the control circuit 40 is operable at step 112 todetermine whether the fill phase of the lockup clutch command, LCC iscomplete and an initial LCC value has been asserted. Illustratively, thetransmission control circuit 40 is operable to execute step 112 bymonitoring the lockup clutch command, LCC, and to determine that thefill phase of the lockup clutch command is complete when the lockupclutch command, e.g., lockup clutch pressure command or other lockupclutch command from which lockup clutch pressure may be determined,drops from the peak fill phase pressure 130 to the initial pressurevalue or initial lockup clutch activation (LCC) value. If thetransmission control circuit 40 determines that the fill phase of thelockup clutch command is not complete, the process 100 loops back tostep 112. If, on the other hand, the transmission control circuit 40determines at step 112 at the fill phase of LCC is complete and theinitial LCC value has been asserted, the process 100 advances to step114 where the transmission control circuit executes a lockup clutchoncoming capacity detection routine.

Referring now to FIG. 4, one illustrative embodiment of the lockupclutch oncoming capacity detection routine 114 is shown. The lockupclutch oncoming capacity detection routine 114 begins at step 150 wherethe transmission control circuit 40 is operable to determine an engineinertia value, I_(E), corresponding to an inertia associated with theengine 12. Illustratively, the engine inertia value, I_(E), is stored inthe memory unit 42, and the transmission control circuit 40 is operableto determine the engine inertia value I_(E), at step 150 by retrievingI_(E) from the memory unit 42. Alternatively, the engine inertia value,I_(E), may be provided to the transmission control circuit 40 by theengine control circuit 66 via the one or more signal paths 64, such asin the form of a message that may be processed by the transmissioncontrol circuit 40 to determine the engine inertia value. Alternativelystill, the transmission control circuit 40 may be operable at step 150to compute the engine inertia value, I_(E), based on one or more engineoperating parameters supplied to the transmission control circuit 40 bythe engine control circuit 66 via the one or more signal paths 64.Further alternatively, the engine control circuit 66 may be operable tocompute the engine inertia value, I_(E), based on one or more engineoperating parameters, and to supply the engine inertia value, I_(E), tothe transmission control circuit 40 at step 150 via the one or moresignal paths 64. In any case, the lockup clutch oncoming capacitydetection routine advances from step 150 to step 152 where thetransmission control circuit 40 is operable to determine an engineoutput torque value, T_(E), corresponding to the output torque producedby the engine 12. Illustratively, the engine output torque value, T_(E),corresponds to an instantaneous value of the engine output torque, andis supplied at step 152 to the transmission control circuit 40 by theengine control circuit 66 via the one or more signal paths 64 asdescribed hereinabove.

Following step 152, the transmission control circuit 40 is operable atstep 154 to compute a compensated engine output torque value, T_(EC), asa function of the instantaneous engine output torque value, T_(E), andthe engine output torque offset value, ΔT_(i), which was computed atstep 110 of the process 100 (see FIG. 2). This embodiment presumes thatany inaccuracies in the engine output torque values, T_(E), supplied bythe engine control circuit 66 are uniform across all engine outputtorque values so that compensating engine output torque values, T_(E),using the engine output torque offset value, ΔT_(i), effectivelyremoves, or at least reduces, such inaccuracies across all engine outputtorque values within typical engine output torque ranges. Conversely, inembodiments in which the engine output torque value, T_(E), produced bythe engine control circuit 66 and supplied by the transmission controlcircuit 40 via the one or more signal paths 64 accurately reflects, orreflects within an acceptable error, the actual torque applied to thepump shaft 16 of the torque converter 20, step 110 of the process 100and step 154 of the routine 114 may be omitted. In this case, the engineoutput torque values, T_(E), supplied by the engine control circuit 66to the transmission control circuit 40 via the one or more signal paths64 may be used by the routine 114. In another alternative embodiment,step 110 of the process 100 and step 154 of the routine 114 may beomitted, and the transmission control circuit 40 may be operable at step152 to determine the engine output torque, T_(E), by estimating thetorque applied to the pump shaft 16 of the torque converter 20 accordingto one or more conventional engine output torque models.

The routine 114 advances from step 154 to step 156 where thetransmission control circuit 40 is operable to determine the pump shaftrotational speed, PS, corresponding to the rotational speed of the pumpshaft 16 of the torque converter 20. The pump shaft rotational speed,PS, may be determined at step 156 by the transmission control circuit 40as described hereinabove with respect to step 106 of the process 100.Following step 156, the transmission control circuit 40 is operable atstep 158 to compute a pump shaft angular acceleration value, PA, as afunction of the pump shaft rotational speed, PS, which was determined atstep 156. Thereafter at step 160, the transmission control circuit 40 isoperable to determine a turbine shaft rotational speed, TS,corresponding to a rotational speed of the turbine shaft 24 of thetorque converter 20. The transmission control circuit 40 isillustratively operable to execute step 160 using any one or more of thetechniques described hereinabove with respect to step 106 of the process100.

Following step 160, the routine 114 advances to step 162 where thetransmission control circuit 40 is operable to compute a lockup clutchtorque value, T_(LU), as a function of I_(E), T_(EC), PS, PA and TS. Inone illustrative embodiment, for example, the transmission controlcircuit 40 is operable to execute step 162 by computing T_(LU) accordingto the model: T_(LU)=T_(EC)−T_(P)−(I_(E)*PA), where T_(P) represents theamount of torque transmitted by the pump 18 of the torque converter 20.Illustratively, T_(P) is computed by the transmission control circuit 40as a function of PS and TS using a model-based transmitted torque modelsuch as, but not limited to, that is described hereinabove with respectto step 108 of the process 100. Alternatively, such as in embodiments inwhich the engine output torque value, T_(E), supplied by the enginecontrol circuit 66 to the transmission control circuit 40 via one ormore of the signal paths 64 is not compensated, the transmission controlcircuit 40 may be operable to determine the lockup clutch torque value,T_(LU), according to the model: T_(LU)=T_(E)−T_(P)−(I_(E)*PA), whereT_(E) represents an uncompensated value of the engine output torque thatmay be determined according to any one or more of the techniquesdescribed hereinabove. In any case, the lockup clutch torque value,T_(LU), computed at step 162 represents an estimate, based on measuredand/or estimated operating values, of the actual torque beingtransmitted by the lockup clutch 32 over time. As it relates to the plotof FIG. 3, the lockup clutch torque estimate, T_(LU), computed at step162 corresponds to the torque being transmitted by the lockup clutch 32during the initial portion of the lockup clutch pressure 128 that occursafter the fill phase and after the initial pressure or initial lockupclutch activation value 132 is asserted. Illustratively, the T_(LU)model is stored in the memory unit 42 of the transmission controlcircuit 40, and the transmission control circuit 40 is operable at step162 to retrieve the T_(LU) model from the memory unit 42, to insertcurrent values of the torque converter operating parameters I_(E),T_(EC) (or T_(E)), PS, PA and TS into the model and to then solve themodel equation for T_(LU).

The routine 114 advances from step 162 to step 164 where thetransmission control circuit 40 is operable to determine whether thelockup clutch torque value, T_(LU), that was computed at step 162 isgreater than a threshold torque value, T_(TH). If not, execution of theroutine 114 loops back to step 152. If, on the other hand, thetransmission control circuit 40 determines at step 164 that the lockupclutch torque value T_(LU) is greater than the threshold torque valueT_(TH), execution of the routine 114 advances to step 166 where thetransmission control circuit 40 is operable to produce a lockup clutchon-coming capacity signal. As used herein, the term “on-coming clutchcapacity” is defined as a condition in which the clutch in question,here the lockup clutch 32, is sufficiently engaged to transmit adiscernable amount of torque. In this regard, the torque threshold,T_(TH), illustratively corresponds to a threshold torque above which thelockup clutch 32 is transmitting a discernable amount of torque. In anycase, the transmission control circuit 40 may be configured to producethe lockup clutch on-coming capacity signal at step 166 by providing acorresponding lockup clutch on-coming capacity value to one or morecontrol algorithms that are being executed by, or that may be executedby, the transmission control circuit 40, by storing a lockup clutchon-coming capacity value in one or more locations in the memory unit 42,by supplying a lockup clutch on-coming capacity signal to the enginecontrol circuit 66 via the one or more signal paths 64, or the like. Inany case, execution of the routine 114 advances from step 166 to step168 where the routine 114 is returned to step routine 114 to the process100 of FIG. 2.

Referring again to FIG. 3, the pump shaft speed 122 generally decreaseswhen engagement of the lockup clutch 32 is being commanded. As the pumpshaft speed 122 decreases toward the turbine speed 126 following thefill phase of the lockup clutch command 128 and subsequent assertion ofthe initial pressure value or initial lockup clutch activation value132, the torque transmitted by the lockup clutch 32 will increaseslightly over time until the lockup clutch 32 begins to transmit adiscernable amount of torque. This point in time is identified in FIG. 3as 134, and corresponds to the point in time, following the fill phaseof the lockup clutch command 128 at which the torque transmitted by thelockup clutch 32 is greater than T_(TH). It is at this point that lockupclutch on-coming capacity is detected. The process illustrated in FIG. 4is operable as just described to continually estimate the lockup clutchtorque, T_(LU), by continually solving the above lockup clutch torquemodel, and to detect lockup clutch on-coming capacity when the estimatedlockup clutch torque, T_(LU), exceeds the torque threshold, T_(TH).

Referring again to FIG. 2, the process 100 advances from step 114 tostep 116 where the transmission control circuit 40 is operable toexecute a lockup clutch control routine. Referring now to FIG. 5, oneillustrative embodiment of the lockup clutch control routine 116 isshown. In the illustrated embodiment, the lockup clutch control routine116 begins at step 180 where the transmission control circuit 40 isoperable to hold the timer 44 (see FIG. 1) in reset. Thereafter at step182, the transmission control circuit 40 is operable to set a countervalue, K, equal to one. Thereafter at step 184, the transmission controlcircuit 40 is operable to execute a pump shaft speed and an accelerationprofile determination routine.

Referring to FIG. 6, one illustrative embodiment of the pump shaft speedand acceleration profile determination routine 184 is shown. In theillustrated embodiment, the pump shaft speed and acceleration profiledetermination routine 184 begins at step 210 where the transmissioncontrol circuit 40 is operable to determine a pump shaft rotationalspeed value, PS_(C), corresponding to the rotational speed of the pump16 of the torque converter 20 at, or just after, detection of on-comingcapacity of the lockup clutch 32 as determined by the lockup clutchon-coming capacity detection routine 114 of FIG. 4. In the plot of FIG.3, for example, the pump shaft rotational speed, PS_(C), is identifiedby the intersection of the dashed vertical line 134 with the pump speedwaveform 122. Following step 210, the transmission control circuit 40 isoperable at step 212 to determine the turbine shaft rotational speed,TS, corresponding to the rotational speed of the turbine shaft 24 of thetorque converter 20 at, or just after, detection of on-coming capacityof the lockup clutch 32. Illustratively, the transmission controlcircuit 40 is operable to determine the pump shaft rotational speed,PS_(C), and the turbine shaft rotational speed, TS, using any of thetechniques described hereinabove.

Following step 212, the transmission control circuit 40 is operable atstep 214 to select a pump speed profile, PSP, and to determine a pumpspeed profile decay rate, DR, as a function of PS_(C), TS and PSP.Illustratively, the pump speed profile, PSP, and decay rate, DR,correspond to a desired decrease, and rate thereof, of the rotationalspeed of the pump shaft 16 of the torque converter 20 from PS_(C) towardthe turbine shaft rotational speed, TS, such that the actual pump shaftrotational speed, PS, achieves synchronous speed with the turbine shaftrotational speed, TS (i.e., at synchronous speed, PS=TS), with a desireddecreasing pump speed profile and decay rate. In the plot of FIG. 3, forexample, the pump speed profile, PSP, 124 between the pump shaftrotational speed, PS_(C), and synchronous speed 137 (PS=TS) is selectedto be linear (the actual, non-linear pump speed 122 is also shown inFIG. 3 between PS_(C) and synchronous speed, PS=TS), although thisdisclosure contemplates embodiments in which PSP is alternativelypiece-wise linear, or nonlinear. The decay rate, DR, of the pump speedprofile, PSP, will generally be selected to achieve synchronous speed(PS=TS) in a reasonable amount of time after detection of on-comingclutch capacity, taking into account the relative difference betweenPS_(C) and TS as well as the selected profile, i.e., shape, of PSP. Thedecay rate, DR, may be constant or non-constant, and selection of thedecay rate, DR, will generally depend upon the application. In any case,the transmission control circuit 40 is operable at step 214 to selectPSP and DR by retrieving PSP and DR from the memory unit 42. It will beunderstood that the memory 42 may be programmed to store any number ofpump speed profiles, PSP, and corresponding decay rate values, DR, andthe transmission control circuit 40 may then be operable at step 214 toselect the pump speed profile and corresponding decay rate value, or anappropriate one of a plurality of pump speed profiles and correspondingdecay rate value based on one or more pre-established criteria.

The routine 184 advances from step 214 to step 216 where thetransmission control circuit 40 is operable to compute a pumpacceleration profile, PAP, as a function of the pump speed profile, PSP,the pump speed PS_(C) and the decay rate, DR. In embodiments in whichthe pump speed profile, PSP, is linear, for example, PAP will be aconstant value. In other embodiments in which the pump speed profile,PSP, is non-linear, PAP will be a function of time. In any case, theroutine 184 advances from step 216 to step 218 where the transmissioncontrol circuit 40 is operable to begin continually computing PSP andPAP at the decay rate DR. Thereafter at step 220, the routine 184 isreturned to the lockup clutch control routine 116 of FIG. 5.

Referring again to FIG. 5, the routine 116 advances from step 184 tostep 186 where the transmission control circuit 40 is operable todetermine the engine output torque, T_(E), using any one of thetechniques described hereinabove. Thereafter at step 188, thetransmission control circuit 40 is operable to compute a compensatedengine output torque value, T_(EC), as described hereinabove withrespect to step 110 of the process 100. Alternatively, in embodiments inwhich T_(EC) is not computed as described hereinabove, step 188 may beomitted from the routine 116. In any case, the transmission controlcircuit 40 is thereafter operable at step 190 to determine the turbineshaft rotational speed, TS, using any one more of techniques describedhereinabove.

Following step 190, the transmission control circuit 40 is operable atstep 192 to execute an accumulator management routine 192. Referring toFIG. 7, one illustrative embodiment of the accumulator managementroutine 192 is shown. In the illustrative embodiment, the accumulatormanagement routine 192 begins at step 250 where the transmission controlcircuit 40 is operable to determine whether the timer 44 (see FIG. 1) isreset. If so, execution of the routine 192 advances to step 252 wherethe transmission control circuit 40 is operable to determine the currentpump shaft rotational speed, PS, and to set a K^(th) value of the pumpspeed, PS_(K), equal to the current value of the pump shaft rotationalspeed, PS. Thereafter at step 254, the transmission control circuit 40is operable to compute a K^(th) value of pump shaft acceleration, PA_(K)as a function of the current number J, of discrete pump shaft speedvalues, where J may accordingly range from one to the current value ofK.

The routine 192 advances from step 254 to step 256 where thetransmission control circuit 40 is operable to determine whether thecurrent or K^(th) value of the pump shaft acceleration, PA_(k), is lessthan the previous value of the pump shaft acceleration, PA_(k-1).Illustratively, PA₀ is set equal to PA₁, so that step 256 advancesthrough the “NO” branch to step 260 when K=1. If, at step 256, thetransmission control circuit 40 determines that PA_(k) is less thanPA_(K-1), the routine 192 advances to step 258 where the transmissioncontrol circuit 40 is operable to set the value of a minimum pump shaftacceleration variable, PA_(MIN), equal to the current value PA_(k), ofthe pump shaft acceleration. If, on the other hand, the transmissioncontrol circuit 40 determines at step 256 that PA_(k) is greater than orequal to PA_(K-1), execution of the routine 192 advances to step 260where the transmission control circuit 40 is operable to determinewhether the difference PA_(k)−PA_(MIN) is greater than an accelerationthreshold value, A_(th). Illustratively, PA_(MIN) is initially set equalto PA₁ so that execution of step 260 advances to the “NO” branch whenK=1. If, at step 260, the transmission control circuit 40 determinesthat the difference PA_(k)−PA_(MIN) is greater than A_(TH), execution ofthe routine 192 advances to step 262 where the transmission circuit 40is operable to hold PSP and PAP at their current values, i.e., todiscontinue computing PSP and PAP at the decay rate, DR, as describedhereinabove with respect to step 218 of the pump shaft speed andacceleration profile determination routine 184. Following step 262, thetransmission control circuit 40 is thereafter operable at step 264 tostart the timer 244 (see FIG. 1). Following step 264, and also followingstep 258, transmission control circuit 40 is operable at step 256 toincrement the value of K by one.

If, at step 250, the transmission control circuit 40 determines that thetimer 44 is not reset, execution of the routine 192 advances to step 268where the transmission control circuit 40 is operable to determine ifthe current value of the timer is greater than an accumulator detectiontime, T_(AD). If so, the transmission control circuit 40 is thereafteroperable at step 270 to resume determining PSP and PAP at the decay rateDR, i.e. to resume computing PSP and PAP at the decay rate DR inaccordance with step 218 of the routine 184 of FIG. 6. Step 266, the“NO” branch of step 268 and step 270 all advance to step 272 where theaccumulator management routine 192 is returned to step 192 of the lockupclutch control routine 116 of FIG. 5.

Referring again to FIG. 5, the lockup clutch control routine 116advances from step 192 to step 194 where the transmission controlcircuit 40 is operable to compute a lockup clutch torque value T_(LU),as a function of I_(E), T_(EC), PSP, PAP and TS. In one illustrativeembodiment, for example, the transmission control circuit 40 is operableto execute step 194 by computing T_(LU) according to the model:T_(LU)=T_(EC)−T_(P)−(I_(E)*PAP), where T_(P) represents the amount oftorque transmitted by the pump 18 of the torque converter 20 with thepump speed profile, PSP, substituted for actual pump speed.Illustratively, T_(P) is computed by the transmission control circuit 40as a function of PSP and TS using a model-based transmitted torque modelsuch as, but not limited to, that is described hereinabove with respectto step 108 of the process 100. Alternatively, such as in embodiments inwhich the engine output torque value, T_(E), supplied by the enginecontrol circuit 66 to the transmission control circuit 40 via one ormore of the signal paths 64 is not compensated, the transmission controlcircuit 40 may be operable to determine the lockup clutch torque value,T_(LU), according to the model: T_(LU)=T_(E)−T_(P)−(I_(E)*PAP), whereT_(E) represents an uncompensated value of the engine output torque thatmay be determined according to any one or more of the techniquesdescribed hereinabove. In any case, the lockup clutch torque valueT_(LU), computed at step 194 corresponds to the amount of torque thatthe lockup clutch 32 would be transmitting under current operatingconditions if the rotational speed and acceleration of the pump shaft 16of the torque converter 20 were equal to the current values of the pumpspeed profile, PSP, and pump acceleration profile, PAP, respectively.Illustratively, the T_(LU) model is stored in the memory unit 42 of thetransmission control circuit 40, and the transmission control circuit 40is operable at step 194 to retrieve the T_(LU) model from the memoryunit 42, to insert current values of the torque converter operatingparameters I_(E), T_(EC) (or T_(E)), PSP, PAP and TS into the model andto then solve the model equation for T_(LU).

Following step 194, the transmission control circuit 40 is operable atstep 196 to modify the lockup clutch command, LCC, that is used tocontrol the actuator 36 (see FIG. 1) based on the lockup clutch torquevalue, T_(LU), computed at step 194. In the embodiment illustrated inFIG. 1, the lockup clutch command, LCC will typically correspond to alockup clutch pressure command, i.e., a command to which the actuator 36is responsive to establish a corresponding fluid pressure in the fluidconduit 34. In this embodiment, the transmission control circuit 40 isoperable to modify LCC based on T_(LU) by converting T_(LU) from unitsof torque to units of pressure and to then use the converted T_(LU)value as the lockup clutch command, LCC. Illustratively, the lockupclutch torque value, T_(LU), may be converted to a lockup clutchpressure value, P_(LU), according to the equation P_(LU)=T_(LU)*G whereG is a gain value and where P_(LU) then corresponds to a lockup clutchpressure command. It will be understood, however, that this disclosurecontemplates embodiments in which the actuator 36 is responsive to alockup clutch torque command to control the lockup clutch 32 to transmita corresponding torque between the pump shaft 16 and the turbine shaft24. In any case, the transmission control circuit 40 is operable toproduce the lockup clutch command, LCC, as a direct function of T_(LU)computed at step 194 or as a direct substitute of T_(LU) for LCC so thatthe model-based lockup clutch torque value, T_(LU), is used to controloperation of the actuator 36. As it relates to the plot of FIG. 3, thelockup clutch torque, T_(LU), computed at step 194 corresponds to theincreasing pressure portion 136 of the lockup clutch command, LCC, 128between PS_(C) (the intersection of the dashed line 124 and the pumpspeed 122) and a delay time following synchronous speed 137.

The lockup clutch control routine 116 advances from step 196 to step 198where the transmission control circuit 40 is operable to determinewhether synchronous speed has been achieved, i.e., whether PS=TS. Ifnot, execution of the lockup clutch control routine 116 loops back tostep 186. If, on the other hand, the transmission control circuit 40determines at step 198 that PS=TS, execution of the lockup clutchcontrol routine 116 advances to step 200 where the lockup clutchcommand, LCC, is commanded to a full or maximum value, LCC_(MAX), aftera time delay, TD, elapses following the determination that PS=TS.Referring once more to FIG. 3, the lockup clutch command, LCC, 128 isshown as being commanded to LCC_(MAX) 138 when a time delay, TD, elapsesfollowing synchronous speed 137. Following step 200, the lockup clutchcontrol routine 116 is returned at step 202 to the process 100 of FIG.2. Referring once more to FIG. 2, the process 100 loops from step 116back to step 104 for continual execution of the process 100.

In an alternative embodiment, a profile and corresponding rate of changefor another one of the torque converter operating parameters that areincluded in the lockup clutch torque model described in the previousparagraph may be determined and substituted for the pump speed profile,PSP, and decay rate, DR. For example, a turbine speed profile may bedetermined in a manner similar to that described with respect to FIG. 6,and a corresponding increase rate may also be determined wherein theturbine speed profile and corresponding increase rate may be selectedsuch that the turbine speed profile increases over time at a desiredrate so as to thereafter achieve synchronous speed by intersecting withthe pump speed. Alternatively still, a profile and corresponding rate ofchange of another one, or a combination of, the torque converteroperating parameters that are included in the lockup clutch torque modeldescribed above may be determined and substituted for PSP and DR. In anysuch alternative embodiments, the profile may be linear, piece-wiselinear or non-linear, and the corresponding rate of change may beconstant or non-constant. The net effect of artificially modifying oneor more of the torque converter operating parameters to solve for T_(LU)would be the same as in the embodiment illustrated in the FIGS., i.e.,to drive the pump speed 122 to synchronous speed (PS=TS) whilecontrollably modifying LCC as a function of T_(LU) whereby engagement ofthe lockup clutch 32 is continually controlled.

Referring now to FIG. 8, operation of the accumulator management routine192 of FIG. 7 will be described with the aid of the illustrated plotwhich is similar to the plot of FIG. 3. In the plot of FIG. 8, the pumpspeed (PS) 280, pump speed profile (PSP) 282, turbine speed (TS) 284 andlockup clutch command (LCC) 286 are all shown vs. time (seconds). Asdescribed with respect to FIG. 3, the lockup clutch command 286 includesa fill phase in which the lockup clutch command 286 is rapidly increasedto a peak value 290 and then rapidly decreased after a short duration ofthe peak value 290 to an initial lockup clutch activation value 292.Lockup clutch on-coming capacity thereafter occurs, and may be detectedaccording to the lockup clutch on-coming capacity detection routine 114of FIG. 4. In relation to FIG. 8, lockup clutch on-coming capacityoccurs where the dashed line 294 intersects the pump speed 280.

Following detection of lockup clutch oncoming capacity, the lockupclutch command 286 is controllably increased, corresponding to theregion 296 of the lockup clutch command 286, such as in accordance withthe lockup clutch control routine 116 of FIG. 5. It has been observedthat as the lockup clutch command, LCC, is controllably increased, e.g.,in the region 296, such as under the control of the lockup clutchcontrol routine 116 of FIG. 5, a short-duration, e.g., 0.1 seconds,accumulator effect may occur during which increases in the lockup clutchcommand 286 have no effect on the actual pump speed 280, i.e., duringwhich increases in the lockup clutch command 128 do not result incorresponding decreases in the actual pump speed 280. The transmissioncontrol circuit 40 is operable, under control of the accumulatormanagement routine 192, to address such accumulator effects bymonitoring the deceleration rate of the pump shaft 16 after detection oflockup clutch on-coming capacity, comparing the pump shaft decelerationrate to a continually-computed maximum pump shaft deceleration rate, andholding the pump speed profile (PSP) and the pump acceleration profile(PAP) constant for a short time duration, e.g., 200 milliseconds, if thepump shaft deceleration rate rises an acceleration threshold, A_(TH),above the maximum pump shaft deceleration rate. As it relates to thelockup clutch control routine 116, the phrase “holding the pump speedprofile (PSP and the pump acceleration profile (PAP) constant for ashort time duration” means temporarily suspending or discontinuing thecontinual computation of PSP and PAP that was begun at step 218 of thepump shaft speed and acceleration profile determination routine 184 ofFIG. 6, and then resuming the continual computation of PSP and PAP afterthe short time duration has elapsed.

The accumulator management routine 192 is executed after lockup clutchon-coming capacity is detected and during each iteration of the lockupclutch control routine 116. The transmission control circuit 40 isoperable at steps 252-254 to compute pump shaft deceleration, PA_(k), asa function of the “J” most recent pump shaft speed signal samples, whereJ ranges from 1 to K, and where K is a counter for the number ofiterations of the main control loop (between steps 186 and 198) of thelockup clutch control routine 116. Steps 256 and 258 then continuallysearch for and establish the maximum deceleration rate, e.g., whichcorresponds to a minimum value of the pump shaft acceleration (PA_(MIN))since deceleration is generally understood to be negative acceleration.The true maximum pump shaft deceleration rate in the example illustratedin FIG. 8 corresponds to the vertical line 298. Step 260 compares thecurrent pump shaft deceleration value, PA_(k), to the most recentmaximum deceleration rate, PA_(MIN), and if the difference is greaterthan the acceleration threshold, A_(TH), the transmission controlcircuit 40 is operable at steps 262 and 264 to hold PSP and PAP constantand to start the timer 44 (FIG. 1). Step 268 checks the timer 44 andwhen the time value of the timer 44 exceeds the accumulator delay time,T_(AD), the transmission control circuit 40 is operable at step 270 toresume continually computing PSP and PAP as begun at step 218 of thepump shaft speed and acceleration profile determination routine 218. Theend of the accumulator time delay, T_(AD), in the example illustrated inFIG. 8 is indicated by the vertical line 300. In between the verticallines 298 and 300, the pump speed profile 282 (dashed-line) is heldconstant as illustrated in FIG. 8. While the actual pump speed 280 andthe pump speed profile 282 may thereafter deviate as shown, increases inthe lockup clutch command 286 will continue to drive the actual pumpspeed 280 toward the turbine speed 284 until synchronous speed 302 isachieved, after which the lockup clutch command 286 may be increased toits maximum, clutch-engaged value 304.

While the invention has been illustrated and described in detail in theforegoing drawings and description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly illustrative embodiments thereof have been shown and described andthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

1. In a torque converter having a pump that is rotatably driven by aninternal combustion engine and that is fluidly coupled to a turbine, anda lockup clutch connected between pump and the turbine, a method fordetecting lockup clutch on-coming capacity, the method comprising:retrieving from memory a dynamic model that defines torque transmittedby the lockup clutch as a function of a plurality of torque converteroperating parameters, asserting a lockup clutch command to controlengagement the lockup clutch, monitoring a number of the plurality oftorque converter operating parameters after asserting the lockup clutchcommand, continually solving the model using the monitored operatingparameters to determine torque transmitted by the lockup clutch overtime, and producing a lockup clutch on-coming capacity signal if thetorque transmitted by the lockup clutch exceeds a torque threshold. 2.The method of claim 1 wherein the lockup clutch command comprises a fillphase followed by an initial lockup clutch activation value, and whereinmonitoring a number of the plurality of torque converter operatingparameters and continually solving the model are carried out after theinitial lockup clutch activation value is asserted.
 3. The method ofclaim 2 further comprising determining inertia of the engine, whereinone of the plurality of torque converter operating parameters includedin the model is the inertia of the engine, and wherein monitoring anumber of the plurality of torque converter operating parameterscomprises monitoring torque applied by the engine to the pump,monitoring rotational speed of the pump, determining angularacceleration of the pump based on the monitored rotational speed of thepump and monitoring rotational speed of the turbine, and wherein themodel defines torque transmitted by the lockup clutch as a function ofthe inertia of the engine, the torque applied by the engine to the pump,the rotational speeds of the pump and the turbine and the angularacceleration of the pump.
 4. The method of claim 3 further comprisingdetermining torque transmitted by the pump as a function of therotational speed of the pump and the rotational speed of the turbine,wherein the dynamic model defines torque transmitted by the lockupclutch according to the equation:T _(LU) =T _(E) −T _(P)−(I _(E) *PA), where T_(LU) is the torquetransmitted by the lockup clutch, T_(E) is the torque applied by theengine to the pump, T_(P) is the torque transmitted by the pump, I_(E)is the inertia of the engine and PA is the angular acceleration of thepump.
 5. The method of claim 3 further comprising: determining aninitial value of the rotational speed of the pump during the fill phaseof the lockup clutch command, determining an initial value of therotational speed of the turbine during the fill phase of the lockupclutch command, receiving an initial value of a reported engine outputtorque produced by a controller during the fill phase of the lockupclutch command, the controller configured to control operation of theengine, and determining a torque offset value as a function of theinitial values of the rotational speed of the pump, the rotational speedof the turbine and the reported engine output torque, and whereinmonitoring torque applied by the engine to the pump comprises monitoringreported engine output torque produced by the controller after theinitial lockup clutch activation value is asserted and computing acompensated engine output torque as a function of the torque offsetvalue and the reported engine output torque produced by the controllerafter the initial lockup clutch activation value is asserted.
 6. Themethod of claim 5 further comprising determining torque transmitted bythe pump as a function of the rotational speed of the pump and therotational speed of the turbine, wherein determining the dynamic modeldefines torque transmitted by the lockup clutch according to theequation:T _(LU) =T _(EC) −T _(P)−(I _(E) *PA), where T_(LU) is the torquetransmitted by the lockup clutch, T_(EC) is the compensated engineoutput torque, T_(P) is the torque transmitted by the pump, I_(E) is theinertia of the engine and PA is the angular acceleration of the pump. 7.In a torque converter having a pump that is rotatably driven by aninternal combustion engine and that is fluidly coupled to a rotatableturbine, and a lockup clutch connected between pump and the turbine, amethod for detecting lockup clutch on-coming capacity, the methodcomprising: determining an inertia of the engine, monitoring torqueapplied by the engine to the pump, monitoring torque transmitted by thepump, monitoring angular acceleration of the pump, continually computingtorque transmitted by the lockup clutch as a function of the inertia ofthe engine, the torque applied by the engine to the pump, the torquetransmitted by the pump, and the angular acceleration of the pump, andproducing a lockup clutch on-coming capacity signal if the torquetransmitted by the lockup clutch exceeds a torque threshold.
 8. Themethod of claim 7 further comprising asserting a lockup clutch commandto engage the lockup clutch, the lockup clutch command including a fillphase followed by an initial lockup clutch activation value, whereinmonitoring torque applied by the engine to the pump, monitoring torquetransmitted by the pump, monitoring angular acceleration of the pump andcontinually computing torque transmitted by the lockup clutch are allcarried out after asserting the initial lockup clutch activation value.9. The method of claim 8 wherein continually computing torquetransmitted by the lockup clutch comprises continually computing thetorque according to the equation:T _(LU) =T _(E) −T _(P)−(I _(E) *PA), where T_(LU) is the torquetransmitted by the lockup clutch, T_(E) is the torque applied by theengine to the pump, T_(P) is the torque transmitted by the pump, I_(E)is the inertia of the engine and PA is the angular acceleration of thepump.
 10. The method of claim 9 further comprising: monitoringrotational speed of the pump, and monitoring rotational speed of theturbine, wherein monitoring torque transmitted by the pump comprisesdetermining the torque transmitted by the pump as a function of therotational speed of the pump and the rotational speed of the turbine.11. The method of claim 7 wherein determining an inertia of the enginecomprises receiving a reported engine inertia value produced by acontrol circuit configured to control operation of the engine.
 12. Themethod of claim 7 wherein determining an inertia of the engine comprisesretrieving a stored engine inertia value from memory.
 13. The method ofclaim 7 further comprising determining a compensated torque value as afunction of a torque offset value and a reported engine output torqueproduced by a controller configured to control operation of the engine,wherein the torque applied by the engine to the pump is the compensatedtorque value.
 14. The method of claim 13 further comprising: asserting alockup clutch command to engage the lockup clutch, the lockup clutchcommand including a fill phase followed by an initial lockup clutchactivation value, and determining the torque offset value by determiningan initial pump rotational speed and an initial turbine rotational speedduring the fill phase of the lockup clutch command, computing an initialpump torque as a function of the initial pump and turbine rotationalspeeds, determining an initial value of the reported engine outputtorque during the fill phase of the lockup clutch command, and computingthe torque offset value as a function of the initial pump torque and theinitial value of the reported engine output torque.
 15. The method ofclaim 14 wherein monitoring torque applied by the engine to the pump,monitoring torque transmitted by the pump, monitoring angularacceleration of the pump and continually computing torque transmitted bythe lockup clutch are all carried out after the initial lockupactivation value is asserted, and wherein continually computing torquetransmitted by the lockup clutch comprises continually computing thetorque according to the equation:T _(LU) =T _(EC) −T _(P)−(I _(E) *PA), where T_(LU) is the torquetransmitted by the lockup clutch, T_(EC) is the compensated torquevalue, T_(P) is the torque transmitted by the pump, I_(E) is the inertiaof the engine and PA is the angular acceleration of the pump.
 16. Themethod of claim 15 further comprising: monitoring rotational speed ofthe pump, and monitoring rotational speed of the turbine, whereinmonitoring torque transmitted by the pump comprises determining thetorque transmitted by the pump as a function of the rotational speed ofthe pump and the rotational speed of the turbine.
 17. A system fordetecting lockup clutch on-coming capacity in a torque converter,comprising: a turbine, a pump engaging an output shaft of an internalcombustion engine and fluidly coupled to the turbine, the lockup clutchconnected between the pump and the turbine, a first sensor configured toproduce a pump speed signal corresponding to a rotational speed of thepump, a second sensor configured to produce a turbine speed signalcorresponding to a rotational speed of the turbine, and a controlcircuit including a memory having instructions stored therein that areexecutable by the control circuit to compute angular acceleration of thepump as a function of the pump speed signal, to compute torquetransmitted by the lockup clutch as a function of the pump speed signal,the turbine speed signal, inertia of the engine, torque applied by theengine to the pump and the angular acceleration of the pump, and toproduce a lockup clutch on-coming capacity signal if the torquetransmitted by the lockup clutch exceeds a threshold torque.
 18. Thesystem of claim 17 further comprising an actuator configured to beresponsive to a lockup clutch activation command to control engagementof the lockup clutch, wherein the instructions stored in the memoryfurther include instructions that are executable by the control circuitto produce the lockup clutch activation command, the lockup clutchactivation command comprising a fill phase followed by an initial lockupclutch activation value.
 19. The system of claim 18 wherein theinstructions stored in the memory further include instructions that areexecutable by the control circuit to begin computing the torquetransmitted by the lockup clutch and comparing the torque transmitted bythe lockup clutch to the threshold torque after the initial lockupclutch activation value is asserted.
 20. The system of claim 19 furthercomprising an engine controller configured to control, at least in part,operation of the engine, wherein the control circuit is configured toreceive engine output torque values, corresponding to torque produced bythe engine, from the engine controller.
 21. The system of claim 20further comprising a data link established between a communication portof the control circuit and a communication port of the enginecontroller, wherein the engine controller is configured to supply theengine output torque values to the data link in the form of engineoutput torque messages, and wherein the control circuit is configured toretrieve the engine output torque messages from the data link.
 22. Thesystem of claim 21 wherein the instructions stored in the memory includeinstructions that are executable by the control circuit to process theengine output torque messages to determine the output torque produced bythe engine.
 23. The system of claim 22 wherein the engine controller isconfigured to supply an inertia value corresponding to the inertia ofthe engine to the data link in the form of an engine inertia message,and wherein the control circuit is configured to retrieve the inertiamessage from the data link and process the inertia message to determinethe inertia of the engine.
 24. The system of claim 22 wherein the memoryhas stored therein a value of the inertia of the engine, and wherein theinstructions stored in the memory further include instructions that areexecutable by the control circuit to determine the inertia of the engineby retrieving the value of the inertia of the engine.
 25. The system ofclaim 22 wherein the instructions stored in the memory includeinstructions that are executable by the control circuit to computetorque transmitted by the pump as a function of the pump speed signaland the turbine speed signal, and to compute the torque transmitted bythe lockup clutch according to the equation:T _(LU) =T _(E) −T _(P)−(I _(E) *PA) where T_(LU) is the torquetransmitted by the lockup clutch, T_(E) is the output torque produced bythe engine, T_(P) is the torque transmitted by the pump, I_(E) is theinertia of the engine and PA is the angular acceleration of the pump.26. The system of claim 21 wherein the instructions stored in the memoryfurther include instructions that are executable by the control circuitto process at least one of the engine output torque messages todetermine an initial engine output torque value, determine from the pumpspeed signal an initial pump speed and determine from the turbine speedsignal an initial turbine speed all during the fill phase of the lockupclutch activation command, and to then compute a torque offset value asa function of the initial engine output torque value, the initial pumpspeed and the initial turbine speed.
 27. The system of claim 26 whereinthe instructions stored in the memory further include instructions thatare executable by the control circuit to determine the output torqueproduced by the engine after the initial lockup clutch activation valueis asserted by processing the engine output torque messages to determinecorresponding engine output torque values, and then computing the outputtorque produced by the engine in the form of a compensated engine outputtorque as a function of the engine output torque values and the torqueoffset value.
 28. The system of claim 27 wherein the engine controlleris configured to supply an inertia value corresponding to the inertia ofthe engine to the data link in the form of an engine inertia message,and wherein the control circuit is configured to retrieve the inertiamessage from the data link and process the inertia message to determinethe inertia of the engine.
 29. The system of claim 27 wherein the memoryhas stored therein a value of the inertia of the engine, and wherein theinstructions stored in the memory further include instructions that areexecutable by the control circuit to determine the inertia of the engineby retrieving the value of the inertia of the engine.
 30. The system ofclaim 27 wherein the instructions stored in the memory includeinstructions that are executable by the control circuit to computetorque transmitted by the pump as a function of the pump speed signaland the turbine speed signal, and to compute the torque transmitted bythe lockup clutch according to the equation:T _(LU) =T _(EC) −T _(P)−(I _(E) *PA) where T_(LU) is the torquetransmitted by the lockup clutch, T_(EC) is the compensated engineoutput torque, T_(P) is the torque transmitted by the pump, I_(E) is theinertia of the engine and PA is the angular acceleration of the pump.